1. Field of the Invention
A current manufacturing process for decorating wallboard panels such as hardboard or particle board applies conventional printing methods, e.g. gravure or silk screen, to decorate a panel substrate with the selected design, and thereafter, a water-resistant, polymeric coating is applied over the decorated substrate. Generally, there are a limited number of colored substrates to which a large variety of designs or decorations are applied. A massive inventory of colored panel substrates, fully decorated panels and decorating inks or dyes are required at each manufacturing and/or warehousing facility.
For example, if a small amount of product having a particular design is ordered, a minimum economic production run may require that 1000 panels be produced to justify the set up costs. The panels produced in excess of the amount required to fill the order must be inventoried, and in some cases it takes many months to sell the "excess" production. In addition, the introduction of a new line of decorated panels requires substantial inventories. Slow moving products often back-up, and panel designs which are being phased out are often difficult to move. The wallboard panel industry needs a low cost manufacturing process which will eliminate product ovrruns and substantially reduce the inventory levels. 2. Description of the Prior Art
The decoration of textile fabrics with sublimable inks or dyes has undergone rapid development during the past ten years. The process is commonly referred to as heat transfer printing wherein a decoration or design is printed on a paper transfer sheet with a subliming dye or ink, and thereafter, the paper is pressed against the textile fabric and heated for a brief period of time whereby the ink is vaporized and transferred to the textile fabric. The dye penetrates into the fabric, forming the design or decoration which was printed on the transfer sheet. This process of heat transfer printing is particularly applicable to knitted polyester fabrics which are very receptive to many subliming dyes. U.S. Pat. No. 3,363,557 illustrates a process for the heat transfer of coloring agents from a transfer sheet to a fabric or other material such as wood, paper, other cellulosic materials, plastic surfaces and even metallic surfaces. This patent does not disclose using the heat transfer printing process to decorate a water-resistant, rigid panel having a clear polymeric coating on one surface.
More recently, U.S. Pat. No. 3,860,388 discloses a method for heat transfer printing with a sublimable dye through a polyolefin release layer to decorate a non-porous thermoplastic sheet or material coated with or bonded to a thermoplastic dye receptor. The method of this patent employs a polyolefin sheet between the dye transfer sheet containing dispersed dyes and the dye receptor thermoplastic material to prevent the printed transfer sheet (paper) from sticking to the thermoplastic dye receptor material. The temperatures employed to sublime or heat transfer the dye are generally sufficient to soften the polyolefin sheet, but it does not stick to the thermoplastic dye receptor material. The method can be used to obtain either high clarity dye transfer, or dye transfer and concurrently lamination of the thermoplastic dye receptor material to a substrate such as hardboard or fiberboard. It appears that in all cases employing a hardboard or fiberboard laminate base material, the dye receptor surface was laminated to the hardboard concurrently with the dye transfer process, and a cured, pre-coated rigid panel was not decorated.
U.S. Pat. No. 3,922,445 discloses a heat transfer printing sheet which can be used to transfer print a variety of base materials. Included in the listed base materials are films and sheets or various synthetic resins, hardboard and gypsum board. There is no disclosure in this patent that a cured, pre-coated rigid panel having a clear, water-resistant polymeric coating can be heat transfer printed.
U.S. Pat. No. 3,952,131, issued on Apr. 20, 1976, discloses a heat transfer print sheet having a polyolefin coating overlying the printed surface to prevent the heat transfer print sheet from adhering to a substrate to which the printing is transferred. The method includes consolidating a plurality of layers of material with heat and pressure, and concurrently therewith, a sublimable dye is transferred from the print sheet to a substrate material. FIG. 3 discloses a finished laminate comprising a polyester film printed with a sublimable dye and laminated to a metalized layer, phenolic impregnated kraft paper and hardboard. There is no disclosure that a cured, precoated rigid panel can be heat transfer printed without requiring a polyolefin layer adjacent to the heat transfer print sheet to prevent adherence to the printed substrate.
There was a series of articles in the American Dyestuff Reporter, February 1975, pp. 23-35, 41, 43-50 and 52-56 disclosing the development of heat transfer printing in the textile fabric industry. Many sublimable dyes are disclosed in these articles and their effectiveness in printing various types of fabric. There is no disclosure that heat transfer printing can be used to decorate a cured, pre-coated rigid panel having a clear, water-resistant polymeric coating on one surface.